[show abstract][hide abstract] ABSTRACT: Rivers with heavy vegetation are hard to map from the air. Here we consider the task of mapping their course and the vegetation along the shores with the specific intent of determining river width and canopy height. A complication in such riverine environments is that only intermittent GPS may be available depending on the thickness of the surrounding canopy. We present a multimodal perception system to be used for the active exploration and mapping of a river from a small rotorcraft flying a few meters above the water. We describe three key components that use computer vision, laser scanning, and inertial sensing to follow the river without the use of a prior map, estimate motion of the rotorcraft, ensure collision- free operation, and create a three dimensional representation of the riverine environment. While the ability to fly simplifies the navigation problem, it also introduces an additional set of constraints in terms of size, weight and power. Hence, our solutions are cognizant of the need to perform multi-kilometer missions with a small payload. We present experimental results along a 2km loop of river using a surrogate system. I. INTRODUCTION We are developing a minimal sensor suite to be used by a low-flying aircraft to autonomously explore rivers, mapping their width and the surrounding canopy. In some cases, the canopy can be so thick and high covering a river that it blocks GPS signals and the problem becomes one of simultaneous localization and mapping in an unstructured fully three- dimensional environment. Exploration from a low-flying vehicle is attractive because it extends the sensing horizon and removes complications of navigating in shallow water and aquatic vegetation. However, a flying solution also adds constraints on the size, weight and power available for per- ception. This is a significant constraint given that the multi- kilometer missions will force all the sensing/computation to be conducted onboard. It is our estimate that given the size of rotorcraft that could reasonably fly in environments with thick canopy, it will be necessary to keep all the sensing and computation components to less than one kilogram. These constraints on payload and the inability to rely on GPS have significant implications for our design. First, we will need to depend on perception to produce a high resolution 6DOF pose estimate that is much more stable than can be produced by simply integrating inertial sensors.
2011 IEEE/RSJ International Conference on Intelligent Robots and Systems, IROS 2011, San Francisco, CA, USA, September 25-30, 2011; 01/2011